> Where did I go wrong?
The following is **wrong** :
$$\frac{\sqrt{x^2-x}}{x}=\sqrt{1-\frac 1x}$$
Note that for $x\lt 0$ $$\frac{\sqrt{x^2-x}}{x}=\frac{\sqrt{x^2(1-\frac 1x)}}{x}=\frac{\sqrt{x^2}\sqrt{1-\frac 1x}}{x}=\frac{|x|\sqrt{1-\frac 1x}}{x}=\frac{\color{red}{-}x\sqrt{1-\frac 1x}}{x}=\color{red}{-}\sqrt{1-\frac 1x}$$